1. Field
The present technology relates to fabrication of semiconductor devices.
2. Description of Related Art
The strong growth in demand for portable consumer electronics is driving the need for high-capacity storage devices. Non-volatile semiconductor memory devices, such as flash memory storage cards, are becoming widely used to meet the ever-growing demands on digital information storage and exchange. Their portability, versatility and rugged design, along with their high reliability and large capacity, have made such memory devices ideal for use in a wide variety of electronic devices, including for example digital cameras, digital music players, video game consoles, PDAs and cellular telephones.
While a wide variety of packaging configurations are known, flash memory storage cards may in general be fabricated as system-in-a-package (SiP) or multichip modules (MCM), where a plurality of die are mounted on a substrate in a stacked configuration. An edge view of a conventional semiconductor package 20 (without molding compound) is shown in prior art FIGS. 1 and 2. Typical packages include a plurality of semiconductor die 22, 24 mounted to a substrate 26. It is known to layer semiconductor die on top of each other either with an offset (prior art FIG. 1) or in a stacked configuration. In a stacked configuration, the die 22, 24 may be separated by a spacer layer 34 (prior art FIG. 2), or by a film layer in which the wire bonds from the lower die may embed. Although not shown in FIGS. 1 and 2, the semiconductor die are formed with die bond pads on an upper surface of the die. Substrate 26 may be formed of an electrically insulating core sandwiched between upper and lower conductive layers.
The upper and/or lower conductive layers may be etched to form conductance patterns including electrical leads and bond fingers. Wire bonds may be bonded between the die bond pads of the semiconductor die 22, 24 and the bond fingers of the substrate 26 to electrically couple the semiconductor die to the substrate. The electrical leads on the substrate in turn provide an electrical path between the die and a host device. Once electrical connections between the die and substrate are made, the assembly is then typically encased in a molding compound to provide a protective package.
As electronic components get smaller and operate at higher frequencies, the noise and cross talk caused by electromagnetic interference (EMI) and radiofrequency interference (RFI) are becoming more of a concern. Electromagnetic radiation is emitted by electrical circuits carrying rapidly changing signals as a by-product of their normal operation. EMI is the induction of electromagnetic radiation to other circuits which causes unwanted signals (interference or noise). RFI is transmission of radiofrequency electromagnetic radiation from one circuit to another, also causing unwanted interference or noise.
Some semiconductor packages have attempted to shield the transmission and receipt of EMI and RFI radiation at the semiconductor package level. While preventing interference, these conventional solutions have other disadvantages which make inclusion of such features at the package level undesirable. Thus, shielding is typically performed at the host device level in which a semiconductor package is used. Host device level solutions typically involve providing a metal shield around the space where a semiconductor package is received or mounted.